[Gate-users] Simulation time for Depth of interaction in PET

[Marc Chamberland]

Hi Leo,

Someone can correct me if I'm wrong, but here are my thoughts:

1) eMultipleScattering is simply the simulation of multiple scattering of a charged particle as it travels through matter. For electrons, this is a big part of the simulation since they have very tortuous paths.

2) If you only care about DOI effect, then I think you can ignore pretty much everything that happens in your phantom. As such, I would use large cuts for electrons and positrons in your phantom. This means that if the electrons or positrons can't move by more than that distance, they'll deposit their energy locally and you won't waste time tracking them. As for multiple scattering, ask yourself if this physical process is important in the DOI effect. I'm not sure myself, but if you're studying this you may have a better idea than me. For example, after your photon is absorbed by photo-electric effect in your crystal, how far do the electrons go? If they do not travel very far, then turning off multiple scattering might be okay.

Also, if you're studying DOI effect, then using a back-to-back source is definitely a good idea to speed up the simulation.

Marc



__________________________

Marc Chamberland, MSc
PhD candidate
Department of Physics
Carleton University
Ottawa (ON)

On 2013-07-30, at 8:20 AM, Leo Read <leoread at gmail.com<mailto:leoread at gmail.com>> wrote:

Hello all,

I'm setting up a simulation to study effect of DOI on point source resolution in a PET detector cylinder based on the PET benchmark code. I'm finding that my simulations are taking a long time.

I tried to turn on/off different processes being modeled in physics.mac and found that commenting out the 'eMultipleScattering' lines in the macro seems to reduce the simulation time significantly. Also, the range of the hits for this process are not very large (typically < 10^-2 mm), which suggests to me that simulating this process is not very important.

Changing the F18LineSource from a e+ emitter to a back-to-back gamma source also helped a lot.

I have two questions:
1) What exactly is 'eMultipleScattering' simulating? The user guide description was not too clear to me.
2) If you were trying to just investigate the effect of DOI on resolution, are there any other changes you would make to the PET benchmark code to save simulation time?

Thanks for your time and comments!
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